Magnetoresistance effect element

ABSTRACT

A magnetoresistance effect element has a first ferromagnetic metal layer, a second ferromagnetic metal layer, and a tunnel barrier layer that is sandwiched between the first and second ferromagnetic metal layers, the tunnel barrier layer is expressed by a chemical formula of AB2Ox, and has a spinel structure in which cations are arranged in a disordered manner, A represents a divalent cation that is either Mg or Zn, and B represents a trivalent cation that includes a plurality of elements selected from the group consisting of Al, Ga, and In.

This application is a divisional of application Ser. No. 15/554,410filed Ang. 29, 2017, which is a National Stage Application ofPCT/JP2016/059884 filed Mar. 28, 2016, which claims priority JapanesePatent Application No. 2015-071410, filed on Mar. 31, 2015, the contentof which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a magnetoresistance effect element.

BACKGROUND ART

Giant magnetoresistance (GMR) elements formed of a multilayer filmconsisting of a ferromagnetic layer and a non-magnetic layer, and tunnelmagnetoresistance (TMR) elements using an insulating layer (a tunnelbarrier layer or a barrier layer) as a non-magnetic layer have beenknown. In general, TMR elements have higher element resistance than GMRelements, but a magnetoresistance (MR) ratio of the TMR elements ishigher than that of the GMR elements. The TMR elements can be dividedinto two types. One type is related to TMR elements using only atunneling effect using an effect of soaking-out of a wave functionbetween ferromagnetic layers. The other type is related to TMR elementsusing coherent tunneling using conduction in a specific orbit of anon-magnetic insulating layer where tunneling is carried out when theabove-described tunneling effect is caused. TMR elements using coherenttunneling have been known to obtain a higher MR ratio than TMR elementsusing only tunneling. The coherent tunneling effect is caused in a casewhere both of the ferromagnetic layer and the non-magnetic insulatinglayer are crystalline and an interface between the ferromagnetic layerand the non-magnetic insulating layer is crystallographicallycontinuous.

Magnetoresistance effect elements are used for various purposes. Forexample, magnetoresistance effect magnetic sensors have been known asmagnetic sensors, and magnetoresistance effect elements determinecharacteristics of a reproducing function of hard disk drives. Magneticsensors have a system that detects, as a resistance change of amagnetoresistance effect element, an effect that a magnetizationdirection of the magnetoresistance effect element is changed by anexternal magnetic field. Highly anticipated devices aremagnetoresistance change-type random access memories (MRAM). MRAMs arememories that read magnetoresistance as digital signals of 0 and 1 byappropriately changing ferromagnetic magnetization directions of twolayers to parallel or antiparallel directions.

LITERATURE Patent Documents

[Patent Document 1] Japanese Patent No. 5586028

[Patent Document 2] Japanese Unexamined Patent Application, FirstPublication No. 2013-175615

Non-Patent Documents

[Non-Patent Document 1] Hiroaki Sukegawa, a [1] Huixin Xiu, TadakatsuOhkubo, Takao Furubayashi, Tomohiko Niizeki, Wenhong Wang, Shinya Kasai,Seiji Mitani, Koichiro Inomata, and Kazuhiro Hono, APPLIED PHYSICSLETTERS 96, 212505 [1] (2010)

[Non-Patent Document 2] Thomas Scheike, Hiroaki Sukegawa, TakaoFurubayashi, Zhenchao Wen, Koichiro inotnata, Tadakatsu Ohkubo, KazuhiroHono, and Seiji Mitani, Applied Physics Letters, 105,242407 (2014)

[Non-Patent Document 3] Yoshio Miura, Shingo Muramoto, Kazutaka Abe, andMasafumi Shirai, Physical Review B 86, 024426 (2012)

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

In recent years, it has been required to use MgO as a non-magneticinsulating layer in order to cause the coherent tunneling. However, in acase where MgO is used as a non-magnetic insulating layer, there is aproblem in that the MR ratio is significantly reduced in a case where abias voltage to be applied to TMR elements is increased.

Future devices such as magnetic sensors and MRAMs are required to obtaina sufficiently high MR ratio even at a high bias voltage. An index for areduction in the MR ratio at a bias voltage is V_(half). V_(half) refersto a bias voltage at which the MR ratio at the time of applying a lowbias voltage is reduced by half with reference to the low bias voltage.The low bias voltage is, for example, 1 mV. Since the optimum low biasvoltage to be obtained varies depending on conditions such as theresistance value of the magnetoresistance effect element, the low biasvoltage may be at least equal to or lower than 1/10 of V_(half).

In a magnetic sensor, an electrical signal obtained as a resistancechange in a circuit should be amplified in order to observe a minutemagnetic field such as geomagnetism or biomagnetism. In order to realizehigher sensitivity than conventional sensors, as well as the MR ratio,an output voltage or an output current should also be increased, anddriving at a high bias voltage is also required. In a case of MRAM,high-voltage driving is required in a write operation. In spin transfertorque-type (STT) MRAMs, the more the magnetization direction of aferromagnetic layer changes, the higher current density is required tobe applied to the magnetoresistance effect element. The magnetizationdirection of a ferromagnetic layer is an effect of the action of aspin-polarized current on the spin of the ferromagnetic layer. Similarlyto the MR ratio, a rewrite-current is generated by a strongspin-polarized current, and thus a high. MR ratio is similarly requiredat a high bias voltage in STT-MRAMs.

In Patent Document 1 and Non Patent Document 1, a tunnel barrier havinga spinel structure is reported to be effective as a substituent materialfor MgO. A spinel tunnel barrier expressed by a composition formula ofMgAl₂O_(x) (0<x≤4) has been known to obtain the same MgO ratio as MgO,and to obtain a higher MR ratio than MgO at a high bias voltage. Inaddition, in Patent Document 2 and Non Patent Documents 2 and 3, thereis a description that MgAl₂O₄ is required to have a disordered spinelstructure in order to obtain a high MR ratio. The above describeddisordered spinel structure denotes a structure where oxygen atoms arearranged in cubic close-packed lattice that is substantially similar tospinel lattice, the structure as a whole belongs to a cubic structure,but arrangement of magnesium and aluminum atoms are disordered. In anoriginal ordered spinel, Mg and Al are arranged in order in thetetrahedral vacancies and octahedral vacancies. However, since these arearranged in a random arrangement in the disordered spinel structure, thecrystal symmetry of the structure is different from MgAl₂O₄, and thelattice constant of the structure is substantially half of 0.808 nm ofMgAl₂O₄.

The invention is contrived in view of the above-described circumstances,and an object thereof is to provide a magnetoresistance effect elementthat obtains a higher MR ratio than TMR elements using a conventionalspinel tunnel barrier at a high bias voltage.

Means for Solving the Problems

In order to solve the above-described problems, a magnetoresistanceeffect element according to one aspect of the invention has a firstferromagnetic metal layer, a second ferromagnetic metal layer, and atunnel barrier layer that is sandwiched between the first and secondferromagnetic metal layers, the tunnel barrier layer is expressed by achemical formula of AB₂O_(x), and has a spinel structure in whichcations are arranged in a disordered manner, A represents a divalentcation that is either Mg or Zn, and B represents a trivalent cation thatincludes a plurality of elements selected from the group consisting ofAl, Ga, and In.

In a case where a different non-magnetic element is disposed in atrivalent cation site of the spinel structure of the tunnel harrierlayer, the basic lattice constant is half the lattice constant of aconventional spinel structure, and the MR ratio is increased.

In the magnetoresistance effect element according to the above aspect,the tunnel barrier layer may have a lattice-matched portion that islattice-matched with both of the first ferromagnetic metal layer and thesecond ferromagnetic metal layer, and a lattice-mismatched portion thatis not lattice-matched with at least one of the first ferromagneticmetal layer and the second ferromagnetic metal layer.

In the magnetoresistance effect element according to the above aspect, avolume ratio of the lattice-matched portion in the tunnel harrier layerwith respect to a volume of the entire tunnel barrier layer may be 65%to 95%.

In a case where the volume ratio of the lattice-matched portion in thetunnel barrier layer is 65% or less, the effect of coherent tunneling isreduced, and thus the MR ratio is reduced. In a case where the volumeratio of the lattice-matched portion in the tunnel barrier layer is 95%or greater, the interference effect between the spin-polarized electronsduring passing through the tunnel barrier layer cannot be weakened, andthus an increase in passage of the spin-polarized electrons through thetunnel barrier layer is not observed. By making the number ofconstituent elements of the non-magnetic element smaller than half thenumber of elements of the aluminum ion, holes are generated in thecations, the holes and two or more types of non-magnetic elements occupythe cations, and thus lattice periodicity is disturbed. Accordingly, theMR ratio is further increased.

In the magnetoresistance effect element according to the above aspect, adifference in ionic radius between the plurality of elements of thetrivalent cation constituting B may be 0.2 Å or less. In a case wherethe difference in ionic radius is small, the cations are unlikely to beordered, and thus the lattice constant becomes smaller than that of ageneral spinel structure. Accordingly, the MR ratio is further increasedin a case of two or more types of elements that are similar to eachother in ionic radius.

In the magnetoresistance effect element according to the above aspect,the number of constituent elements in a unit cell of the divalent cationmay be smaller than half that of the trivalent cation. By making thenumber of constituent elements of the non-magnetic element smaller thanhalf that of the trivalent cation, holes are generated in the cations,the holes and two or more types of non-magnetic elements occupy thecations, and thus lattice periodicity is disturbed. Accordingly, the MRratio is increased.

In the magnetoresistance effect element according to the above aspect, amagnetoresistance ratio may be 100% or greater under application of avoltage of 1 V or greater at a room temperature. The magnetoresistanceeffect element can also be used in devices to which a high bias voltageis applied, such as high-sensitivity magnetic sensors,logic-in-memories, and MRAMs.

In the magnetoresistance effect element according to the above aspect,the first ferromagnetic metal layer may have larger coercivity than thesecond ferromagnetic metal layer. Since the coercivity of the firstferromagnetic metal layer is different from that of the secondferromagnetic metal layer, the element functions as a spin valve, anddevice application is possible.

In the magnetoresistance effect element according to the above aspect,at least one of the first ferromagnetic metal layer and the secondferromagnetic metal layer may have magnetic anisotropy perpendicular toa stacking direction. Since it is not necessary to apply a bias magneticfield, it is possible to reduce the device in size. In addition, theelement can be allowed to function as a recording element since it hashigh thermal disturbance resistance.

In the magnetoresistance effect element according to the above aspect,at least one of the first ferromagnetic metal layer and the secondferromagnetic metal layer may be Co₂Mn_(1-a)Fe_(a)Al_(b)Si_(1-b) (0≤a≤1,0≤b≤1). Co₂Mn_(1-a)Fe_(a)Al_(b)Si_(1-b) is a ferromagnetic metalmaterial having high spin polarizability, and a higher MR ratio can beobtained than in a case where another ferromagnetic metal material isused.

In the magnetoresistance effect element according to the above aspect,in the trivalent cation, a proportion of any one of Al, Ga, or In as amain component may be 85% to less than 100%. In a region where theproportion of any one of Al, Ga, or In as a main component is 85% toless than 100%, RA is lower than in a case where the proportion of themain component is 100%. Regarding this, it can be thought that thesubstituted element imparts distortion to the crystal lattice, and thusa component contributing to conduction is imparted. Otherwise, thesubstituted element is thought to form an impurity level in a bandgapand to contribute to conduction.

Effects of the Invention

According to the above aspects of the present invention, it is possibleto provide a magnetoresistance effect element that obtains a higher MRratio than TMR elements using a conventional spinel tunnel barrier at ahigh bias voltage.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a stacked structure of a magnetoresistance effect element.

FIG. 2 is a diagram of a crystal structure of a spinel.

FIG. 3 is a schematic diagram of an ordered spinel structure and adisordered spinel structure with symmetry of Fm-3m having a latticeconstant assumed in a tunnel barrier layer of the invention.

FIG. 4 is a schematic diagram of an ordered spinel structure and adisordered spinel structure with symmetry of Fm-3m having a latticeconstant assumed in a tunnel barrier layer of the invention.

FIG. 5 is a schematic diagram of an ordered spinel structure and adisordered spinel structure with symmetry of Fm-3m having a latticeconstant assumed in a tunnel barrier layer of the invention.

FIG. 6 is a schematic diagram of an ordered spinel structure and adisordered spinel structure with symmetry of F-43m having a latticeconstant assumed in a tunnel barrier layer of the invention.

FIG. 7 is a schematic diagram of an ordered spinel structure and adisordered spinel structure with symmetry of F-43m having a latticeconstant assumed in a tunnel barrier layer of the invention.

FIG. 8 is a diagram showing a structure to be evaluated of amagnetoresistance effect element according to an embodiment in adirection perpendicular to a stacking direction.

FIG. 9 is a diagram showing the element structure according to theembodiment when seen from the stacking direction.

FIG. 10 is a graph showing results of evaluation of a magnetoresistanceeffect of a magnetoresistance effect element of Example 1.

FIG. 11 is a diagram showing results of evaluation of bias voltagedependency of the magnetoresistance effect of the magnetoresistanceeffect element of Example 1.

FIG. 12 is a diagram showing results of evaluation of bias voltagedependency of a magnetoresistance effect of a magnetoresistance effectelement of Example 2.

FIG. 13 is a diagram showing results of evaluation of bias voltagedependency of a magnetoresistance effect of a magnetoresistance effectelement of Example 3.

FIG. 14 is a diagram showing results of evaluation of bias voltagedependency of a magnetoresistance effect of a magnetoresistance effectelement of Example 4.

FIG. 15 is a diagram showing results of evaluation of bias voltagedependency of a magnetoresistance effect of a magnetoresistance effectelement of Example 5.

FIG. 16 is a diagram showing results of evaluation of bias voltagedependency of a magnetoresistance effect of a magnetoresistance effectelement of Example 6.

FIG. 17 is a diagram showing results of evaluation of bias voltagedependency of a magnetoresistance effect of a magnetoresistance effectelement of Example 7.

FIG. 18 is a diagram obtained by plotting RA obtained from results ofmeasurement of a magnetoresistance effect of Example 8 and the amount ofGa in trivalent cations obtained from EDS.

FIG. 19 is a diagram showing results of evaluation of bias voltagedependency of a magnetoresistance effect of a magnetoresistance effectelement of Comparative Example 1.

FIG. 20 is a diagram showing results of evaluation of bias voltagedependency of a magnetoresistance effect of a magnetoresistance effectelement of Comparative Example 2.

FIGS. 21(A) and 21(B) show an example of a part in which the tunnelbarrier layer and the ferromagnetic metal layer are lattice-matched.FIG. 21(A) shows a high-resolution cross-section TEM. FIG. 21(B) showsan example of an image obtained by performing inverse Fourier analysis.

FIG. 22 is a diagram showing a structure of a cross-section when seenfrom a including a direction parallel to a stacking direction of Example9.

FIGS. 23(A), 23(B) and 23(C) are diagrams showing a proportion of alattice-matched portion in which a tunnel barrier layer of Example 9 islattice-matched with both of a first ferromagnetic metal layer and asecond ferromagnetic metal layer, and characteristics of an element.FIG. 23(A) is a diagram showing element resistance (Rp) whenmagnetization directions of the first ferromagnetic metal layer and thesecond ferromagnetic metal layer are parallel to each other. FIG. 23(B)is a diagram showing element resistance (Rap) when magnetizationdirections of the first ferromagnetic metal layer and the secondferromagnetic metal layer are antiparallel to each other. FIG. 23(C) isa diagram showing a magnetoresistance ratio of the element.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the invention will be described in detailwith reference to the accompanying drawings. In the description of thedrawings, the same elements will be denoted by the same referencenumerals, and an overlapping description thereof will be omitted.

First Embodiment

Hereinafter, a case where a magnetoresistance effect element accordingto a first embodiment has a first ferromagnetic metal layer 6, a secondferromagnetic metal layer 7, and a tunnel barrier layer 3 sandwichedbetween the first and second ferromagnetic metal layers, and the tunnelbarrier layer 3 is expressed by a chemical formula of AB₂O_(x) (0<x≤4),has a spinel structure in which cations are arranged in a disorderedmanner, and contains a divalent cation that is either Mg or Zn and atrivalent cation that includes a plurality of elements selected from thegroup consisting of Al, Ga, and In will be described.

(Basic Structure)

In the example shown in FIG. 1, a magnetoresistance effect element 100is provided on a substrate 1, and has a stacked structure provided withan underlayer 2, a first ferromagnetic metal layer 6, a tunnel barrierlayer 3, a second ferromagnetic metal layer 7, and a cap layer 4 inorder from the substrate 1.

(Tunnel Barrier Layer)

The tunnel barrier layer 3 is made of a non-magnetic insulatingmaterial. In general, the tunnel barrier layer has a film thickness of 3nm or less, and in a case where the tunnel barrier layer is sandwichedbetween metal materials, a wave function of electrons of atoms of themetal materials extends beyond the tunnel barrier layer 3, and thus acurrent may flow regardless of the presence of an insulating material onthe circuit. The magnetoresistance effect element 100 is classified intotwo types including: a type in which the typical tunneling effect isused; and a type in which the coherent tunneling effect where an orbitfor tunneling is limited is predominant. In the typical tunnelingeffect, a magnetoresistance effect is obtained by spin polarization offerromagnetic materials. On the other hand, in the coherent tunneling,an orbit for tunneling is limited. Therefore, in a magnetoresistanceeffect element in which coherent tunneling is predominant, an effecthigher than or equivalent to spin polarization of ferromagnetic metalmaterials can be expected. In order to exhibit the coherent tunnelingeffect, it is necessary that the ferromagnetic metal materials and thetunnel barrier layer 3 be crystallized and joined in a specificorientation.

(Spinel Structure)

FIG. 2 shows a spinel structure. An A-site in which oxygen is fourfoldcoordinated to cations and a B-site in which oxygen is sixfoldcoordinated to cations exist. Here, a Sukenel structure referring to thespinel structure in which cations are disordered is a structure that hasa lattice constant half the lattice constant of an ordered spinelstructure while a position of an oxygen atom of the ordered spinel isalmost not changed, and in which cations are positioned in tetrahedralpositions and octahedral positions of oxygen atoms that are not occupiedunder ordinary circumstances. At this time, this structure may includetotal five structures shown in FIGS. 3 to 7, and may be any one of themor a mixed structure thereof.

(Definition of Disordered Spinel Structure)

In this specification, the spinel structure in which cations aredisordered may be referred to as a Sukenel structure. The Sukenelstructure refers to a structure where oxygen atoms are arranged in cubicclose-packed lattice that is substantially similar to spinel lattice,the structure as a whole belongs to a cubic structure, but arrangementof cations are disordered. In an original ordered spinel, Mg and Al arearranged in order in the tetrahedral vacancies and octahedral vacanciesin the original spinel. However, since these are arranged in randomarrangement in the Sukenel structure, the crystal symmetry of thestructure is different from MgAl₂O₄, and the lattice constant of thestructure is substantially half of that of MgAl₂O₄. With a change in thelattice-repeating unit, a combination between the ferromagnetic layermaterial and the electronic structure (band structure) is changed, andthus a large TMR enhancement due to a coherent tunneling effect isobtained. For example, a space group of MgAl₂O₄ that is a non-magneticspinel material is Fd-3m, but a space group of a disordered spinelstructure with a lattice constant reduced by half is known to be changedto Fm-3m or F-43m, and there are total five structures (Non-PatentDocument 2). Any one of them can be used.

In this specification, the Sukenel structure is not essentially requiredto be a cubic structure. In the stacked structure, the crystal structureis influenced by the crystal structure of the material of an underlayer,and the lattice is thus partially distorted. Each material has a bulkcrystal structure, but in a case where it is formed into a thin film, apartially distorted crystal structure based on the bulk crystalstructure can be taken. Particularly, in the invention, the tunnelbarrier layer has a very thin structure, and is easily influenced by thecrystal structure of the layer brought into contact with the tunnelbarrier layer. In this regard, the bulk crystal structure of a Sukenelstructure is a cubic structure, and in this specification, the Sukenelstructure includes a Sukenel structure which does not have a cubicstructure in addition to a Sukenel structure slightly deviating from thecubic structure. A deviation from the cubic structure in the Sukenelstructure described in this specification is generally slight, and thisdeviation depends on the accuracy of a measurement method for evaluatingthe structure.

The divalent cation (A-site) in the non-magnetic element of the tunnelbarrier layer is either magnesium or zinc. These nonmagnetic elementsare stable in a case where the number of valence is 2, and in a casewhere these non-magnetic elements are constituent elements of the tunnelbarrier layer, coherent tunneling can be realized, and the MR ratio isincreased.

The trivalent cation (B-site) in the non-magnetic element of the tunnelbarrier layer includes at least two types of elements selected from thegroup consisting of aluminum, gallium, and indium. These non-magneticelements are stable in a case where the number of valence is 3, and in acase where these non-magnetic elements are constituent elements of thetunnel barrier layer, coherent tunneling can be realized, and the MRratio is increased.

A difference in ionic radius between the trivalent cations of theplurality of non-magnetic elements of the tunnel barrier layer may be0.2 A or less. In a case where the difference in ionic radius is small,the cations are unlikely to be ordered, and thus the lattice constantbecomes smaller than that of a general spinel structure. Accordingly,the MR ratio is further increased in a case of two or more types ofelements that are similar to each other in ionic radius.

In the trivalent cations of the tunnel barrier layer, the proportion ofany one of Al, Ga, or In as a main component may be 85% to less than100%. In a region where the proportion of any one of Al, Ga, or In as amain component is 85% to less than 100%, RA is lower than in a casewhere the proportion of the main component is 100%. Regarding this, itcan be thought that the substituted element imparts distortion to thecrystal lattice, and thus a component contributing to conduction isimparted. Otherwise, the substituted element is thought to form animpurity level in a bandgap and to contribute to conduction.

(First Ferromagnetic Metal Layer)

Examples of the material of the first ferromagnetic metal layer 6include metal selected from the group consisting of Cr, Mn, Co, Fe, andNi, alloy including one or more of the metals of the group, and alloyincluding one or more metals selected from the group and at least oneelement of B, C, and N. Specific examples thereof include Co—Fe andCo—Fe—B. A Heusler alloy such as Co₂FeSi is preferable in order toobtain a high output. The Heusler alloy includes intermetallic compoundshaving a chemical composition of X₂YZ. X denotes a Co, Fe, Ni, or Cugroup transition metal element or noble metal in the periodic table, Ydenotes a Mn, V, Cr, or Ti group transition metal, and can also take theelemental species of X, and Z denotes representative elements of III toV groups. Examples thereof include Co₂FeSi, Co₂MnSi, andCo₂Mn_(1-a)Fe_(a)Al_(b)Si_(1-b). In addition, an antiferromagneticmaterial such as IrMn and PtMn may be used as a material brought intocontact with the first ferromagnetic metal layer 6 in order to makecoercivity of the first ferromagnetic metal layer larger than that ofthe second ferromagnetic metal layer 7. Furthermore, the firstferromagnetic metal layer may have a synthetic ferromagnetic couplingstructure such that the second ferromagnetic metal layer 7 is notinfluenced by a leakage magnetic field of the first ferromagnetic metallayer 6.

In a case where a magnetization direction of the first ferromagneticmetal layer 6 is made perpendicular to the stacked plane, a stacked filmof Co and Pt is preferably used. For example, in a case where the firstferromagnetic metal layer 6 has a composition of [Co (0.24 nm)/Pt (0.16nm)]₆/Ru (0.9 nm)/[Pt (0.16 nm)/Co (0.16 nm)]₄/Ta (0.2 nm)/FeB (1.0 nm),the magnetization direction can be made perpendicular to the stackedplane.

(Second Ferromagnetic Metal Layer)

A ferromagnetic material, particularly, a soft magnetic material isapplied as a material of the second ferromagnetic metal layer 7, andexamples thereof include metal selected from the group consisting of Cr,Mn, Co, Fe, and Ni, alloy including one or more of the metals of thegroup, and alloy including one or more metals selected from the groupand at least one element of B, C, and N. Specific examples thereofinclude Co—Fe, Co—Fe—B, and Ni—Fe.

In a case where a magnetization direction of the second ferromagneticmetal layer 7 is made perpendicular to the stacked plane, the secondferromagnetic metal layer 7 preferably has a thickness of 2.5 nm orless. Perpendicular magnetic anisotropy can be applied to the secondferromagnetic metal layer 7 at an interface between the secondferromagnetic metal layer 7 and the tunnel barrier layer 3. The secondferromagnetic metal layer 7 preferably has a thin film thickness sincethe effect of the perpendicular magnetic anisotropy is reduced if thesecond fenomagnetic metal layer 7 has a thick film thickness.

In general, the first ferromagnetic metal layer 6 has a structure inwhich the magnetization direction thereof is fixed, and is called afixed layer. In addition, since the second ferromagnetic metal layer 7has a magnetization direction that can be more easily changed by anexternal magnetic field or a spin torque than the first ferromagneticmetal layer 6, the second ferromagnetic metal layer is called a freelayer.

(Substrate)

A magnetoresistance effect element according to the invention may beformed on a substrate.

In that case, a material showing excellent flatness is preferably usedas a material of the substrate 1. The substrate 1 differs depending onthe purpose. For example, in a case of MRAM, a circuit formed in a Sisubstrate can be used under the magnetoresistance effect element. In acase of a magnetic head, an AlTiC substrate that can be easily processedcan be used.

(Underlayer)

In a case where a magnetoresistance effect element according to theinvention is formed on a substrate, first, an underlayer may be formedon the substrate.

In that case, the underlayer 2 is used to control crystallinity such ascrystal orientation and crystal grain size of the first ferromagneticmetal layer 6 and layers formed above the first ferromagnetic metallayer 6. Therefore, it is important to select the material of theunderlayer 2. Hereinafter, the material and the configuration of theunderlayer 2 will be described. Any of a conductive material and aninsulating material may be used for the underlayer, but in a case whereelectric power is fed to the underlayer, a conductive material ispreferably used. First, as a first example of the underlayer 2, anitride layer having a (001)-oriented NaCl structure and containing atleast one element selected from the group consisting of Ti, Zr, Nb, V,Hf, Ta, Mo, W, B, Al, and Ce is exemplified. As a second example of theunderlayer 2, a (002)-oriented perovskite conductive oxide layer made ofABO₃ is exemplified. Here, the A-site includes at least one elementselected from the group consisting of Sr, Ce, Dy, La, K, Ca, Na, Pb, andBa, and the B-site, includes at least one element selected from thegroup consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Nb, Mo, Ru, Ir, Ta,Ce, and Pb. As a third example of the underlayer 2, an oxide layerhaving a (001)-oriented NaCl structure and containing at least oneelement selected from the group consisting of Mg, Al, and Ce isexemplified. As a fourth example of the underlayer 2, a layer having a(001)-oriented tetragonal or cubic structure and containing at least oneelement selected from the group consisting of Al, Cr, Fe, Co, Rh, Pd,Ag, Ir, Pt, Au, Mo, and W is exemplified. As a fifth example of theunderlayer 2, a layer having a stacked structure with a combination oftwo or more of the layers of the above first to fourth examples isexemplified. By devising the structure of the underlayer as describedabove, it is possible to control the crystallinity of the ferromagneticlayer 2 and layers formed above the ferromagnetic layer 2, therebyimproving the magnetic characteristics.

(Cap Layer)

A cap layer may be formed on the second ferromagnetic metal layer of themagnetoresistance effect element according to the invention.

A cap layer 4 is installed above the second ferromagnetic metal layer 7in a stacking direction in order to control crystallinity such ascrystal orientation and crystal grain size and element diffusion. In acase where a free layer having a bee structure is formed, the crystalstructure of the cap layer may be any one of a fcc structure, a hepstructure, and a bee structure. In a case where a free layer having afcc structure is formed, the crystal structure of the cap layer may beany one of a fee structure, a hep structure, and a bcc structure. Thefilm thickness of the cap layer may be within such a range that adistortion relaxation effect is obtained and a reduction in the MR ratioby shunt is not shown. The film thickness of the cap layer is preferably1 nm to 30 nm.

(Shape and Dimensions of Element)

A laminate formed of the first ferromagnetic metal layer, the tunnelbarrier layer, and the second ferromagnetic metal layer 2 constitutingthe invention has a columnar shape. In addition, it may have variousshapes such as a circular shape, a square shape, a triangle shape, and apolygonal shape when viewed from top, and preferably has a circularshape from the viewpoint of symmetry. That is, the laminate preferablyhas a columnar shape.

FIGS. 8 and 9 show examples of the shape and the dimensions of themagnetoresistance effect element.

FIG. 8 is a diagram showing a structure when viewed from a side in astacking direction of the magnetoresistance effect element 100. Themagnetoresistance effect element 100 of FIG. 8 has an electrode layer 5formed above the cap layer 4 shown in FIG. 1. FIG. 9 is a diagramshowing a structure when viewed in the stacking direction of themagnetoresistance effect element 100. In FIG. 9, a current source 71 anda voltmeter 72 are also shown.

The magnetoresistance effect element 100 is processed into a columnarshape of 80 nm or less as shown in FIGS. 8 and 9, and wiring is applied.Since the magnetoresistance effect element 100 is processed into acolumnar shape having a size of 80 nm or less, a domain structure is notlikely to be formed in the ferromagnetic metal layers, and it is notnecessary to consider a component having a different spin polarizationin the ferromagnetic metal layers. In FIG. 9, the magnetoresistanceeffect element 100 is disposed at a position where the underlayer 2 andthe electrode layer 5 intersect each other.

(Evaluation Method)

The magnetoresistance effect element 100 can be evaluated with thestructure shown in FIGS. 8 and 9. For example, the power supply 71 andthe voltmeter 72 are disposed as shown in FIG. 9 such that a fixedcurrent or a fixed voltage is applied to the magnetoresistance effectelement 100. By measuring the voltage or the current while sweeping anexternal magnetic field, a change in the resistance of themagnetoresistance effect element 100 can be measured.

In general, the MR ratio is expressed by the following formula.

MR Ratio(%)={(R _(AP) −R _(P))/R _(P)}×100

R_(P) denotes a resistance in a case where magnetization directions ofthe first ferromagnetic metal layer 6 and the second ferromagnetic metal7 are parallel to each other, and R_(AP) denotes a resistance in a casewhere magnetization directions of the first ferromagnetic metal layer 6and the second ferromagnetic metal 7 are antiparallel to each other.

In a case where a strong current flows in the magnetoresistance effectelement 100, magnetization rotation occurs by a STT effect, and aresistance value of the magnetoresistance effect element 100 is rapidlychanged. The current value at which the resistance value is rapidlychanged is called an inversion current value (Jc).

(Others)

In this example, a structure in which the first ferromagnetic metallayer 6 having high coercivity is disposed on the lower side is anexemplary example of this structure, but the invention is not limited tothis structure. In a case of a structure in which the firstferromagnetic metal layer 6 having high coercivity is disposed on theupper side, the coercivity is reduced in comparison with a case in whichthe first ferromagnetic metal layer 6 is disposed on the lower side, butthe tunnel barrier layer 3 can be formed by utilizing the crystallinityof the substrate, and thus the MR ratio can be increased.

In order to utilize the magnetoresistance effect element as a magneticsensor, a resistance change preferably changes linearly with respect toan external magnetic field. In a general stacked film of ferromagneticlayers, magnetization directions are easily directed into the stackedplane by shape anisotropy. In this case, for example, a magnetic fieldis applied from outside to make the magnetization directions of thefirst ferromagnetic metal layer and the second ferromagnetic metal layerintersect each other, thereby changing the resistance change linearlywith respect to the external magnetic field. However, in this case,since a mechanism that applies a magnetic field is required near themagnetoresistance effect element, this is not preferable forintegration. In a case where the ferromagnetic metal layer itself hasperpendicular magnetic anisotropy, this is advantageous for integrationsince a method such as application of a magnetic field from outside isnot required.

The magnetoresistance effect element using this embodiment can be usedas a magnetic sensor or a memory such as a MRAM. Particularly, thisembodiment is effective for products that are used with a bias voltagehigher than a bias voltage used in conventional magnetic sensors.

(Manufacturing Method)

The magnetoresistance effect element 100 can be formed using, forexample, a magnetron sputtering apparatus.

The tunnel barrier layer 3 can be produced through a known method. Forexample, a thin metal film is formed on the first ferromagnetic metallayer 6 by sputtering, performing plasma oxidation or natural oxidationby oxygen introduction thereon; and performing a heat treatment thereon.As the film-forming method, not only a magnetron sputtering method butalso a thin film-forming method such as a vapor deposition method, alaser ablation method, or a MBE method can be used.

Each of the underlayer, the first ferromagnetic metal layer, the secondferromagnetic metal layer, and the cap layer can be formed through aknown method.

Second Embodiment

A second embodiment is different from the first embodiment only in themethod of forming a tunnel barrier layer. In the first embodiment, thetunnel barrier layer is formed by repeatedly performing formation andoxidation of a metal film. In the second embodiment, the substratetemperature is lowered to −70 to −30 degrees, and then oxidation isperformed in the oxidation step. By cooling the substrate, a temperaturegradient is generated between the substrate and the vacuum or betweenthe substrate and the plasma. First, in a case where a surface of thesubstrate is exposed to oxygen, oxygen reacts with the metal materialand the metal material is oxidized. However, the oxidation does notproceed due to the low temperature. Accordingly, the oxygen amount ofthe tunnel barrier layer is easily adjusted. Moreover, by forming thetemperature gradient, epitaxial growth (lattice-matched growth) iseasily adjusted. Since the crystal growth proceeds by the temperaturegradient, the epitaxial growth is easily performed in a case where thetemperature of the substrate is sufficiently lowered. As the temperatureof the substrate is increased, domains are formed and a plurality ofcrystal nuclei are thus formed in the plane. Each of the crystal nucleiis independently and epitaxially grown, and thus a part in whichlattices are not matched is formed in a part in which the grown domainsare in contact with each other.

It is preferable that in the tunnel barrier layer, lattice-matchedparts, which are lattice-matched with both of a first ferromagneticmetal layer and a second ferromagnetic metal layer, partially exist. Ingeneral, it is preferable that the tunnel barrier layer be completelylattice-matched to both of the first ferromagnetic metal layer and thesecond ferromagnetic metal layer. However, in a case where the tunnelbarrier layer is completely lattice-matched, spin-polarized electronsinterfere with each other during passing through the tunnel barrierlayer, and thus the electrons do not easily pass through the tunnelbarrier layer. In contrast, in a case where lattice-matched parts, inwhich lattices are matched, partially exist, the interference betweenspin-polarized electrons during passing through the tunnel barrier layeris appropriately cut in parts in which lattices are not matched, andthus the spin-polarized electrons easily pass through the tunnel barrierlayer. The volume ratio of the lattice-matched part portion in thetunnel barrier layer with respect to the volume of the entire tunnelbarrier layer is preferably 65% to 95%. In a case where the volume ratioof the lattice-matched part in the tunnel barrier layer is 65% or less,the effect of coherent tunneling is reduced, and thus the MR ratiodecreases. In a case where the volume ratio of the lattice-matched partin the tunnel barrier layer is 95% or greater, the interference effectbetween the spin-polarized electrons during passing through the tunnelbarrier layer is not be weakened, and thus an increase in passage of thespin-polarized electrons through the tunnel barrier layer is notobserved.

(Method of Calculating Volume Ratio of Lattice-Matched Portion)

The volume ratio of the lattice-matched part (lattice-matched portion)with respect to the volume of the entire tunnel barrier layer can beestimated from, for example, a TEM image. Regarding whether the latticesare matched, a part including the tunnel barrier layer, the firstferromagnetic metal layer, and the second ferromagnetic metal layer in across-section TEM image is Fourier-transformed to obtain an electronbeam diffraction image. In the electron beam diffraction image obtainedby Fourier transformation, electron beam diffraction spots in directionsother than the stacking direction are removed. That image is subjectedto inverse Fourier transformation to provide an image in whichinformation only in the stacking direction is obtained. In lattice linesin the inverse Fourier image, a part in which the tunnel barrier layeris continuously connected to both of the first ferromagnetic metal layerand the second ferromagnetic metal layer is defined as a lattice-matchedportion. In addition, in lattice lines, a part in which the tunnelbarrier layer is not continuously connected to at least one of the firstferromagnetic metal layer and the second ferromagnetic metal layer, orin which no lattice lines are detected is defined as alattice-mismatched portion. In the lattice-matched portion, in thelattice lines in the inverse Fourier image, the layers are continuouslyconnected from the first ferromagnetic metal layer to the secondferromagnetic metal layer via the tunnel barrier layer, and thus a width(L_(C)) of the lattice-matched portion can be measured from the TEMimage. Similarly, in the lattice-mismatched portion, in the latticelines in the inverse Fourier image, the layers are not continuouslyconnected, and thus a width (L_(I)) of the lattice-mismatched portioncat be measured from the TEM image. Using the width (L_(C)) of thelattice-matched portion as a numerator and using the sum of the width(L_(C)) of the lattice-matched portion and the width (L_(I)) of thelattice-mismatched portion as a denominator, the volume ratio of thelattice-matched portion with respect to the volume of the entire tunnelbarrier layer can be obtained. The TEM image is a cross-section image,but includes information including a depth. Accordingly, it can bethought that the region estimated from the TEM image is proportional tothe volume.

FIGS. 21(A) and 21(B) show an example of the part in which the tunnelbarrier layer and the ferromagnetic metal layer are lattice-matched.FIG. 21(A) shows an example of a high-resolution cross-section TEMimage. FIG. 21(B) shows an example of an image obtained by performinginverse Fourier transformation after removal of electron beamdiffraction spots in directions other than the stacking direction in theelectron beam diffraction image. In FIG. 21(B), components perpendicularto the stacking direction are removed, and thus lattice lines can beobserved in the stacking direction. This shows that the tunnel barrierlayer and the ferromagnetic metal layer are continuously connected toeach other without interruption at an interface therebetween.

EXAMPLES Example 1

Hereinafter, an example of the method of manufacturing amagnetoresistance effect element according to the first embodiment willbe described. Film formation was performed on a substrate provided witha thermal silicon oxide film using a magnetron sputtering method. As anunderlayer, 5 nm of Ta/3 nm of Ru was formed, and as a firstferromagnetic metal layer, 12 nm of IrMn/10 nm of CoFe/0.8 nm of Ru/7 nmof CoFe was formed in this order on the underlayer. Next, a method offorming a tunnel barrier layer will be shown. A film of 0.1 nm of Mg/0.4nm of Mg_(0.5)Al_(1.0)Ga_(1.1)In_(0.9) was formed by sputtering with aMg target and a target having an alloy composition ofMg_(0.5)Al_(1.0)Ga_(1.1)In_(0.9). Thereafter, the above-described samplewas moved to an oxidation chamber of which the inside was kept in anultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation byintroducing Ar and oxygen. The natural oxidation time was 10 seconds,the partial pressure ratio of Ar to oxygen was 1 to 25, and the totalgas pressure was 0.05 Pa. Then, the sample was returned to afilm-forming chamber, and a film of 0.05 nm of Mg/0.3 nm ofMg_(0.5)Al_(1.0)Ga_(1.1)In_(0.9)/0.05 nm of Mg was formed. Theabove-described sample was moved to the oxidation chamber of which theinside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to performnatural oxidation and inductively coupled plasma oxidation byintroducing Ar and oxygen. The natural oxidation time was 30 seconds,and the inductively coupled plasma oxidation time was 5 seconds. Thepartial pressure ratio of Ar to oxygen was 1 to 20, and the total gaspressure was 0.08 Pa.

The above-described stacked film was moved again to the film-formingchamber, and a 5 nm CoFe film was formed as a second ferromagnetic metallayer 7. 3 nm of Ru/5 nm of Ta was formed as a cap layer 4.

The above-described stacked film was installed in an annealingapparatus, and heated at a temperature of 450° C. in Ar atmosphere for10 minutes. Thereafter, under an applied field of 8 kOe, a heattreatment was performed on the stacked film at 280 degrees for 6 hours.

Next, an element was formed as in FIG. 9. First, a photoresist wasformed using electron beam lithography in such a way that the electrodelayer was in a direction rotated by 90 degrees as in FIG. 9. A partother than a part below the photoresist was eliminated by an ion millingmethod to expose the thermal silicon oxide film that was the substrate,and thus a shape of the underlayer 2 was formed. In a narrow part in theshape of the underlayer, a photoresist was formed into a columnar shapeof 80 nm using electron beam lithography, and a part other than a partbelow the photoresist was eliminated by an ion milling method to exposethe underlayer. Thereafter, SiOx was formed as an insulating layer onthe part shaved by ion milling. Here, the photoresist with a columnarshape of 80 nm was removed. The photoresist was not formed only in apart corresponding to an electrode pad of FIG. 9, and the insulatinglayer was removed by an ion milling method to expose the underlayer.Thereafter, an Au layer was formed. This electrode pad 8 functions as acontact electrode for the underlayer of the above-described stackedfilm. Next, a photoresist was formed and shaping was performed by an ionmilling method such that the electrode layer of FIG. 9 was formed, andan Au film was formed. This functions as a contact electrode for theelectrode layer of the above-described stacked film.

Characteristic Evaluation of Example 1

The magnetoresistance effect element evaluation method is based on amagnetoresistance effect element evaluation method that has beengenerally performed. As shown in FIG. 9, a current source and avoltmeter were connected to the electrode pad and the electrode layer,respectively, to perform measurement by a four-terminal method. A biasvoltage to be applied from the voltmeter was appropriately changed to 10to 1500 mV, and a current was measured by the current source to obtain aresistance value. The changing resistance value was observed by applyinga magnetic field to the magnetoresistance effect element from outside.FIG. 10 is a diagram showing results of the evaluation of themagnetoresistance effect of the magnetoresistance effect element ofExample 1. The horizontal axis represents a magnetic field, and thevertical axis represents the resistance of the element. The bias voltageapplied was 1 V, and electrons flowed in a direction from the firstferromagnetic metal layer to the second ferromagnetic layer 7. From FIG.10, it was found that the MR ratio was 79.0%, and the area resistance(RA) of the element was 0.75 Ω·μm². FIG. 11 is a diagram showing resultsof the evaluation of bias voltage dependency of the magnetoresistanceeffect of the magnetoresistance effect element of Example 1. It is foundthat in the magnetoresistance effect element of Example 1, the MR ratiois reduced with an increase in the bias voltage. From FIG. 11, it isfound that the voltage (V_(half)) at which the MR ratio is reduced byhalf is 1 V.

Structure Analysis of Example 1

For structure analysis of the tunnel barrier layer, evaluation wasperformed with an electron diffraction image obtained using transmissionelectron beams. The structure of the barrier layer was examined throughthis method, and it was confirmed that there was no reflection from the{022} plane and the {111} plane shown in the ordered spinel structure.In addition, it was found that this barrier had a cubic structure inwhich the spinel structure was disordered.

Composition Analysis of Example 1

The composition of the tunnel barrier layer was analyzed using energydispersive X-ray analysis (EDS). As a standard of the composition ratio,the sum of the contents of Al, Ga, and In was defined as 2, and relativeamounts of Mg and Zn were compared to each other. As a result,Mg:Al:Ga:In=1.0:0.67:0.73:0.6 was obtained. Quantitativity of oxygen wasignored since it is difficult to perform quantitative evaluation ofoxygen. In general, the crystal structure can be maintained even in acase where the amount of oxygen deviates from the quantitative ratio inan oxide.

Example 2

The production method is similar to that in Example 1, but only thematerial for forming the tunnel barrier layer is different from that ofExample 1. A film of 0.1 nm of Zn/0.4 nm ofZn_(0.5)Al_(1.0)Ga_(1.1)In_(0.9) was formed by sputtering with a Zntarget and a target having an alloy composition ofZn_(0.5)Al_(1.0)Ga_(1.1)In_(0.9). Thereafter, the above-described samplewas moved to an oxidation chamber of which the inside was kept in anultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation byintroducing Ar and oxygen. The natural oxidation time was 10 seconds,the partial pressure ratio of Ar to oxygen was 1 to 25, and the totalgas pressure was 0.05 Pa. Then, the sample was returned to afilm-forming chamber, and a film of 0.05 nm of Zn/0.3 nm ofMg_(0.5)Al_(1.0)Ga_(1.1)In_(0.9)/0.05 nm of Zn was formed. Theabove-described sample was moved to the oxidation chamber of which theinside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to performnatural oxidation and inductively coupled plasma oxidation byintroducing Ar and oxygen. The natural oxidation time was 30 seconds,and the inductively coupled plasma oxidation time was 5 seconds. Thepartial pressure ratio of Ar to oxygen was I to 20, and the total gaspressure was 0.08 Pa.

Characteristics of Example 2

As a result of the measurement of the magnetoresistance effect, it wasfound that in a case where the bias voltage was 1 V, the MR ratio was85.6%, and the area resistance (RA) of the element was 0.72 Ω·μm². FIG.12 is a diagram showing results of the evaluation of bias voltagedependency of the magnetoresistance effect of the magnetoresistanceeffect element of Example 2. It is found that in the magnetoresistanceeffect element of Example 2, the MR ratio is reduced with an increase inthe bias voltage. From FIG. 12, it is found that the voltage (V_(half))at which the MR ratio is reduced by half is 1.1 V. Relative amounts werecompared to each other using EDS, and the result wasZn:Al:Ga:In=1.05:0.65:0.75:0.6. In addition, a cubic structure in whichthe spinel structure was disordered was confirmed from an electron beamdiffraction image.

Example 3

The production method is similar to that in the Example 1, but only thematerial for forming the tunnel barrier layer is different from that ofExample 1. A film of 0.1 nm of Mg/0.4 nm of Mg_(0.5)Al_(1.9)Ga_(1.1) wasformed by sputtering with a Mg target and a target having an alloycomposition of Mg_(0.5)Al_(1.9)Ga_(1.1). Thereafter, the above-describedsample was moved to an oxidation chamber of which the inside was kept inan ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation byintroducing Ar and oxygen. The natural oxidation time was 10 seconds,the partial pressure ratio of Ar to oxygen was 1 to 25, and the totalgas pressure was 0.05 Pa. Then, the sample was returned to afilm-forming chamber, and a film of 0.05 nm of Mg/0.3 nm ofMg_(0.5)Al_(1.9)Ga_(1.1)/0.05 nm of Mg was formed. The above-describedsample was moved to the oxidation chamber of which the inside was keptin an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidationand inductively coupled plasma oxidation by introducing Ar and oxygen.The natural oxidation time was 30 seconds, and the inductively coupledplasma oxidation time was 5 seconds. The partial pressure ratio of Ar tooxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

Characteristics of Example 3

As a result of the measurement of the magnetoresistance effect, it wasfound that in a case where the bias voltage was 1 V, the MR ratio was128.5%, and the area resistance (RA) of the element was 0.69 Ω·μm². FIG.13 is a diagram showing results of the evaluation of bias voltagedependency of the magnetoresistance effect of the magnetoresistanceeffect element of Example 3. It is found that in the magnetoresistanceeffect element of Example 2, the MR ratio is reduced with an increase inthe bias voltage. From FIG. 13, it is found that the voltage (V_(half))at which the MR ratio is reduced by half is 1.35 V. Relative amountswere compared to each other using EDS, and the result wasMg:Al:Ga=1.0:1.35:0.65. In addition, a cubic structure in which thespinel structure was disordered was confirmed from an electron beamdiffraction image.

Example 4

The production method is similar to that in the Example 1, but only thematerial for forming the tunnel barrier layer is different from that ofExample 1. A film of 0.1 nm of Mg/0.4 nm of Mg_(0.5)Al_(1.9)In_(1.1) wasformed by sputtering with a Mg target and a target having an alloycomposition of Mg_(0.5)Al_(1.9)In_(1.1). Thereafter, the above-describedsample was moved to an oxidation chamber of which the inside was kept inan ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation byintroducing Ar and oxygen. The natural oxidation time was 10 seconds,the partial pressure ratio of Ar to oxygen was 1 to 25, and the totalgas pressure was 0.05 Pa. Then, the sample was returned to afilm-forming chamber, and a film of 0.05 nm of Mg/0.3 nm ofMg_(0.5)Al_(1.9)In_(1.1)/0.05 nm of Mg was formed. The above-describedsample was moved to the oxidation chamber of which the inside was keptin an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidationand inductively coupled plasma oxidation by introducing Ar and oxygen.The natural oxidation time was 30 seconds, and the inductively coupledplasma oxidation time was 5 seconds. The partial pressure ratio of Ar tooxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

Characteristics of Example 4

As a result of the measurement of the magnetoresistance effect, it wasfound that in a case where the bias voltage was 1 V, the MR ratio was70%, and the area resistance (RA) of the element was 0.67 Ω·μm². FIG. 14is a diagram showing results of the evaluation of bias voltagedependency of the magnetoresistance effect of the magnetoresistanceeffect element of Example 4. It is found that in the magnetoresistanceeffect element of Example 4, the MR ratio is reduced with an increase inthe bias voltage. From FIG. 14, it is found that the voltage (V_(half))at which the MR ratio is reduced by half is 1 V. Relative amounts werecompared to each other using EDS, and the result wasMg:Al:In=1.0:1.4:0.58. In addition, a cubic structure in which thespinel structure was disordered was confirmed from an electron beamdiffraction image.

Example 5

The production method is similar to that in the Example 1, but only thematerial for forming the tunnel barrier layer is different from that ofExample 1. A film of 0.1 nm of Mg/0.4 nm of Mg_(0.5)Ga_(1.5)In_(1.5) wasformed by sputtering with a Mg target and a target having an alloycomposition of Mg_(0.5)Ga_(1.5)In_(1.5). Thereafter, the above-describedsample was moved to an oxidation chamber of which the inside was kept inan ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation byintroducing Ar and oxygen. The natural oxidation time was 10 seconds,the partial pressure ratio of Ar to oxygen was 1 to 25, and the totalgas pressure was 0.05 Pa. Then, the sample was returned to afilm-forming chamber, and a film of 0.05 nm of Mg/0.3 nm ofMg_(0.5)Ga_(1.5)In_(1.5)/0.05 nm of Mg was formed. The above-describedsample was moved to the oxidation chamber of which the inside was keptin an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidationand inductively coupled plasma oxidation by introducing Ar and oxygen.The natural oxidation time was 30 seconds, and the inductively coupledplasma oxidation time was 5 seconds. The partial pressure ratio of Ar tooxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

Characteristics of Example 5

As a result of the measurement of the magnetoresistance effect, it wasfound that in a case where the bias voltage was 1 V, the MR ratio was132%, and the area resistance (RA) of the element was 0.65 Ω·μm². FIG.15 is a diagram showing results of the evaluation of bias voltagedependency of the magnetoresistance effect of the magnetoresistanceeffect element of Example 5. It is found that in the magnetoresistanceeffect element of Example 5, the MR ratio is reduced with an increase inthe bias voltage. From FIG. 15, it is found that the voltage (V_(half))at which the MR ratio is reduced by half is 1.5 V. Relative amounts werecompared to each other using EDS, and the result wasMg:Ga:In=1.0:1.1:0.9. In addition, a cubic structure in which the spinelstructure was disordered was confirmed from an electron beam diffractionimage.

Example 6

The production method is similar to that in the Example 1, but only thematerial for forming the tunnel barrier layer is different from that ofExample 1. A film of 0.05 nm Mg/0.4 nm of Mg_(0.5)Ga_(1.5)In_(1.5) wasformed by sputtering a Mg target and a target having an alloycomposition of Mg_(0.5)Ga_(1.5)In_(1.5). Thereafter, the above-describedsample was moved to an oxidation chamber of which the inside was kept inan ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation byintroducing Ar and oxygen. The natural oxidation time was 10 seconds,the partial pressure ratio of Ar to oxygen was 1 to 25, and the totalgas pressure was 0.05 Pa. Then, the sample was returned to afilm-forming chamber, and a film of 0.05 nm of Mg/0.3 mu ofMg_(0.5)Ga_(1.5)In_(1.5)/0.05 nm of Mg was formed. The above-describedsample was moved to the oxidation chamber of which the inside was keptin an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidationand inductively coupled plasma oxidation by introducing Ar and oxygen.The natural oxidation time was 30 seconds, and the inductively coupledplasma oxidation time was 5 seconds. The partial pressure ratio of: r tooxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

Characteristics of Example 6

As a result of the measurement of the magnetoresistance effect, it wasfound that in a case where the bias voltage was 1 V, the MR ratio was146%, and the area resistance (RA) of the element was 0.62 Ω·μm². FIG.16 is a diagram showing results of the evaluation of bias voltagedependency of the magnetoresistance effect of the magnetoresistanceeffect element of Example 6. It is found that in the magnetoresistanceeffect element of Example 6, the MR ratio is reduced with an increase inthe bias voltage. From FIG. 16, it is found that the voltage (V_(half))at which the MR ratio is reduced by half is 1.5 V. Relative amounts werecompared to each other using EDS, and the result wasMg:Ga:In=0.83:1.05:0.96. In addition, a cubic structure in which thespinel structure was disordered was confirmed from an electron beamdiffraction image.

Example 7

The production method is similar to that in Example 6, but only thematerial for forming the first ferromagnetic metal layer is differentfrom Example 6. A material having an alloy composition ofCo₂Mn_(0.7)Fe_(0.3)Si_(0.66)Al_(0.36) was used in place of CoFe to forma film. 12 nm of IrMn/10 nm of CoFe/0.8 nm of Ru/2 nm of CoFe/5 nm ofCo₂Mn_(0.7)Fe_(0.3)Si_(0.66)Al_(0.36) was formed in order as the firstferromagnetic metal layer. Only when a film was formed using thematerial having an alloy composition ofCo₂Mn_(0.7)Fe_(0.3)Si_(0.66)Al_(0.36), the substrate was heated at 450degrees. In addition, before the formation of the tunnel barrier layer,the heat of the substrate was sufficiently radiated to lower thetemperature of the substrate to about the room temperature, and then thesubsequent film forming process was performed.

Characteristics of Example 7

As a result of the measurement of the magnetoresistance effect, it wasfound that in a case where the bias voltage was 1 V, the MR ratio was182%, and the area resistance (RA) of the element was 0.65 Ω·μm². FIG.17 is a diagram showing results of the evaluation of bias voltagedependency of the magnetoresistance effect of the magnetoresistanceeffect element of Example 7. It is found that in the magnetoresistanceeffect element of Example 5, the MR ratio is reduced with an increase inthe bias voltage. From FIG. 17, it is found that the voltage (V_(half))at which the MR ratio is reduced by half is 1.25 V. In addition, a cubicstructure in which the spinel structure was disordered was confirmedfrom an electron beam diffraction image.

Example 8

The production method is similar to that in Example 1, but only thematerial for forming the tunnel barrier layer is different from Example1, a film with a thickness of 0.5 nm was formed by simultaneouslysputtering with a target having an alloy composition of Mg_(0.9)Al₂ anda target having an alloy composition of Mg_(0.9)Ga₂. At this time, thecontents of Al and Ga were adjusted so as to obtain an arbitrarycomposition ratio. Thereafter, the above-described sample was moved toan oxidation chamber of which the inside was kept in an ultrahigh vacuumof 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar andoxygen. The natural oxidation time was 10 seconds, the partial pressureratio of Ar to oxygen was 1 to 25, and the total gas pressure was 0.05Pa. Then, the sample was returned to a film-forming chamber, and atarget having an alloy composition of Mg_(0.9)Al₂ and a film with athickness of 0.4 nm was formed by simultaneously sputtering with atarget having an alloy composition of Mg_(0.9)Ga₂. At this time, thecontents of Al and Ga were adjusted so as to obtain an arbitrarycomposition ratio. The above-described sample was moved to the oxidationchamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Paor less to perform natural oxidation and inductively coupled plasmaoxidation by introducing Ar and oxygen. The natural oxidation time was30 seconds, and the inductively coupled plasma oxidation time was 5seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and thetotal gas pressure was 0.08 Pa.

Characteristics of Example 8

FIG. 18 is a diagram obtained by plotting RA obtained from the resultsof the measurement of the magnetoresistance effect of Example 8 and theamount of Ga in the trivalent cations obtained from EDS. The compositionratio of Al to the sum of Mg and Zn was confirmed to be 0.9:2 at anycomposition ratio. The bias voltage is 1 V. In addition, a cubicstructure in which the spinel structure was disordered was confirmedfrom an electron beam diffraction image. From FIG. 18, it is found thatat a composition ratio of Mg_(0.9)(Al_(1−x)Ga_(x))₂O₄, a region where RAis rapidly reduced is present in a region where a concentration x of Gais greater than 0 and equal to or less than 0.2 and in a region wherethe concentration x of Ga is equal to or greater than 0.85. In addition,it is found that a minimum value is shown in a case where theconcentration x of Ga is 0.06 and 0.93. In a region where the proportionof any one of Al, Ga, or In as a main component is 85% to less than100%, RA is lower than in a case where the proportion of the maincomponent is 100%. Regarding this, it can be thought that thesubstituted element imparts distortion to the crystal lattice, and thusa component contributing to conduction is imparted. Otherwise, thesubstituted element is thought to form an impurity level in a bandgapand to contribute to conduction.

Example 9

The production method is similar to that in Example 3, but only themethod for forming the tunnel harrier layer is different from Example 3.Film formation was performed on a substrate provided with a thermalsilicon oxide film using a magnetron sputtering method. A film of 0.1 nmof Mg/0.4 nm of Mg_(0.5)Al_(1.9)Ga_(1.1) was formed by sputtering with aMg target and a target having an alloy composition ofMg_(0.5)Al_(1.9)Ga_(1.1). Thereafter, the above-described sample wasmoved to an oxidation chamber of which the inside was kept in anultrahigh vacuum of 1×10⁻⁸ Pa or less, and the substrate was cooled to−70 to −30 degrees. Then, natural oxidation was performed by introducingAr and oxygen. The natural oxidation time was 10 seconds, the partialpressure ratio of Ar to oxygen was 1 to 25, and the total gas pressurewas 0.05 Pa. Then, the sample was returned to a film-forming chamber,and a film of 0.05 nm of Mg/0.3 nm of Mg_(0.5)Al_(1.9)Ga_(1.1)/0.05 nmof Mg was formed. The above-described sample was moved to the oxidationchamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Paor less, and the substrate was cooled to −70 to −30 degrees. Then,natural oxidation and inductively coupled plasma oxidation wereperformed by introducing Ar and oxygen. The natural oxidation time was30 seconds, and the inductively coupled plasma oxidation time was 5seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and thetotal gas pressure was 0.08 Pa.

Cross-Section Analysis of Example 9

A volume ratio of the lattice-matched part (lattice-matched portion)with respect to the volume of the entire tunnel barrier layer wascalculated as described above using a cross-section transmissionelectron microscope (TEM) image and an image obtained by removingelectron beam diffraction spots in a direction other than a stackingdirection in an electron beam diffraction image obtained byFourier-transforming the TEM image and by then performing inverseFourier transformation.

FIG. 22 is a structural schematic diagram of a cross-section including adirection parallel to the stacking direction of Example 9. From thehigh-resolution cross-section TEM image obtained in Example 9, it wasfound that a size (width) of the film surface of the lattice-matchedpart of the tunnel barrier layer in a direction parallel thereto was 30nm or less in any part. 30 nm is approximately 10 times the latticeconstant of the CoFe alloy that is the material of the firstferromagnetic metal layer and the second ferromagnetic metal layer, andmutual interference of the spin-polarized electrons in a directionperpendicular to the tunneling direction before or after coherenttunneling can be thought to be intensified approximately 10 times thelattice constant.

FIGS. 23(A), 23(B) and 23(C) are diagrams showing a volume ratio of thelattice-matched part (lattice-matched portion) with respect to thevolume of the entire tunnel barrier layer of Example 9 andcharacteristics of the element. FIG. 23(A) is a diagram showing elementresistance (Rp) when magnetization directions of the first ferromagneticmetal layer and the second ferromagnetic metal layer are parallel toeach other. FIG. 23(B) is a diagram showing element resistance (Rap)when magnetization directions of the first ferromagnetic metal layer andthe second ferromagnetic metal layer are antiparallel to each other.FIG. 23(C) is a diagram showing a magneto resistance ratio of theelement. The Rp tends to be reduced when the proportion of thelattice-matched part in which the tunnel barrier layer islattice-matched to both of the first ferromagnetic metal layer and thesecond ferromagnetic metal layer is in the range of 65% to 95%.Regarding this, in a case where the tunnel barrier layer is completelylattice-matched, spin-polarized electrons interfere with each otherduring passing through the tunnel barrier layer, and thus it is thoughtthat the electrons do not easily pass through the tunnel barrier layer.In contrast, in a case where the lattice-matched parts, in whichlattices are matched, partially exists, the interference ofspin-polarized electrons during passing through the tunnel barrier layeris appropriately cut in a part in which lattices are not matched, andthus the spin-polarized electrons easily pass through the tunnel barrierlayer. As a result, it is thought that a tendency of a reduction in theRp is observed. At the same time, a tendency of a slight increase in theRap is observed when the proportion of the lattice-matched portion is inthe range of 65% to 95%. This indicates that even when the magnetizationdirections of the first ferromagnetic metal layer and the secondferromagnetic metal layer are antiparallel to each other, theinterference between domains is eased, and it is found that thespin-polarized electrons passing through the tunnel barrier layer aremagnetically scattered.

Comparative Example 1

The production method is similar to that in Example 1, but only thematerial for forming the tunnel barrier layer is different fromExample 1. A film of Mg with a thickness of 0.45 nm was formed bysputtering with a Mg target. Thereafter, the above-described sample wasmoved to an oxidation chamber of which the inside was kept in anultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation byintroducing Ar and oxygen. The natural oxidation time was 10 seconds,the partial pressure ratio of Ar to oxygen was 1 to 25, and the totalgas pressure was 0.05 Pa. Then, the sample was returned to afilm-forming chamber, and a film of Mg with a thickness of 0.4 nm wasformed. The above-described sample was moved to the oxidation chamber ofwhich the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less toperform natural oxidation and inductively coupled plasma oxidation byintroducing Ar and oxygen. The natural oxidation time was 30 seconds,and the inductively coupled plasma oxidation time was 5 seconds. Thepartial pressure ratio of Ar to oxygen was 1 to 20, and the total gaspressure was 0.08 Pa.

Characteristics of Comparative Example 1

As a result of the measurement of the magnetoresistance effect, it wasfound that in a case where the bias voltage was 1 V, the MR ratio was27%, and the area resistance (RA) of the element was 0.6 Ω·μm². FIG. 19is a diagram showing results of the evaluation of bias voltagedependency of the magnetoresistance effect of the magnetoresistanceeffect element of comparative Example 1. It is found that in themagnetoresistance effect element of Comparative Example 1, the MR ratiois reduced with an increase in the bias voltage. From FIG. 19, it isfound that the voltage (V_(half)) at which the MR ratio is reduced byhalf is 0.45 V. In addition, a spinel structure was confirmed from anelectron beam diffraction image.

Comparative Example 2

The production method is similar to that in Example 1, but only thematerial for forming the tunnel barrier layer is different from Example1, a film of 0.05 nm of Mg/0.05 nm of Zn/10.25 nm ofMg_(0.15)Zn_(0.25)Al₂/0.1 nm of Al was formed by sputtering with a Mgtarget, an Al target, and a target having an alloy composition ofMg_(0.5)Zn_(0.5)Al₂. Thereafter, the above-described sample was moved toan oxidation chamber of which the inside was kept in an ultrahigh vacuumof 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar andoxygen. The natural oxidation time was 10 seconds, the partial pressureratio of Ar to oxygen was 1 to 25, and the total gas pressure was 0.05Pa. Then, the sample was returned to a film-forming chamber, and a filmof 0.05 nm/0.05 nm of Zn/0.2 nm of Mg_(0.15)Zn_(0.25)Al₂/0.1 nm of Alwas formed. The above-described sample was moved to the oxidationchamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Paor less to perform natural oxidation and inductively coupled plasmaoxidation by introducing Ar and oxygen. The natural oxidation time was30 seconds, and the inductively coupled plasma oxidation time was 5seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and thetotal gas pressure was 0.08 Pa.

Characteristics of Comparative Example 2

As a result of the measurement of the magnetoresistance effect, it wasfound that in a case where the bias voltage was 1 V, the MR ratio was46%, and the area resistance (RA) of the element was 0.8 Ω·μm². FIG. 20is a diagram showing results of the evaluation of bias voltagedependency of the magnetoresistance effect of the magnetoresistanceeffect element of comparative Example 2. It is found that in themagnetoresistance effect element of Comparative Example 2, the MR ratiois reduced with an increase in the bias voltage. From FIG. 20, it isfound that the voltage (V_(half)) at which the MR ratio is reduced byhalf is 0.7 V. Relative amounts were compared to each other using EDS,and the result was Mg:Zn:Al=0.5:0.5:2. In addition, a spinel structurewas confirmed from an electron beam diffraction image.

Comparison of Examples with Comparative Examples

Table 1 shows the examples and the comparative examples.

TABLE 1 RA [Ω · μm²] MR Ratio [%] V_(half) [V] EXAMPLES EXAMPLE 1 0.7579 1.0 EXAMPLE 2 0.72 85 1.1 EXAMPLE 3 0.69 128 1.35 EXAMPLE 4 0.67 691.0 EXAMPLE 5 0.65 132 1.5 EXAMPLE 6 0.62 146 1.5 EXAMPLE 7 0.62 1821.25 COMPARATIVE EXAMPLES COMPARATIVE 0.59 27 0.45 EXAMPLES 1COMPARATIVE 0.80 46 0.70 EXAMPLES 2

In a case that Examples are compared with Comparative Examples, it isfound that Examples have better characteristics than ComparativeExamples in terms of both of the MR ratio and V_(half). Particularly, inExamples, V_(half) is improved approximately twice in comparison to acase where MgMg₂O₄ of Comparative Example 2 is used for a tunnel barrierlayer. In addition, there is a tendency that the RA is reduced and theMR ratio is improved by substituting a part of Al³⁺ with gallium orindium.

Examples can be divided into two types. One type is related to Examplesin which some trivalent cations are substituted with gallium and indium.The other type, related to Examples in which some trivalent cations aresubstituted with gallium or indium, or a part of Ga³⁺ is substitutedwith indium. Regarding one of these types, in Examples in which a partof Al³⁺ is substituted with gallium or indium, or Ga³⁺ is partiallysubstituted with indium, the MR ratio is higher and V_(half) is alsohigher than in the examples in which some trivalent cations aresubstituted with gallium and indium. In addition, in Example 4, the MRratio is low. Here, the ionic radiuses of the trivalent cations areshown in Table 2.

TABLE 2 ION IONIC RADIUS [Å] Al³⁺ 0.535 Ga³⁺ 0.62 In³⁺ 0.8

The value of the ionic radius is quoted from Non Patent Document 2. InExamples 1, 2, and 4, the difference in ionic radius between thetrivalent cations contained in the tunnel barrier layer is up to 0.265Å, and in Examples 3, 5, 6, and 7, the difference in ionic radiusbetween the trivalent cations is up to 0.18 Å. In a case where thedifference in ionic radius is small, there is no reason for the cationsto be periodically arranged since these are regarded to be equivalent inthe crystal structure. Thus, the trivalent cations are randomly disposedin the crystal. In a case where the difference in ionic radius is large,the cations are relaxed as much as possible in the crystal lattice, andthus the crystal lattice is stabilized in a case where the cations areperiodically arranged. That is, the trivalent cations are likely to beperiodically arranged. From these facts, it is found that thecharacteristics are improved in a case where the difference in ionicradius between the divalent cations of the plural non-magnetic elementsis 0.2 Å or less.

INDUSTRIAL APPLICABILITY

The invention can be applied to a magnetoresistance effect clement thatobtains a higher MR ratio than TMR elements using a conventional spineltunnel barrier at a high bias voltage.

DESCRIPTION OF THE REFERENCE SYMBOLS

-   100: MAGNETORESISTANCE EFFECT ELEMENT-   1: SUBSTRATE-   2: UNDERLAYER-   3: TUNNEL BARRIER LAYER-   4: CAP LAYER-   5: ELECTRODE LAYER-   6: FIRST FERROMAGNETIC METAL LAYER-   7: SECOND FERROMAGNETIC METAL LAYER-   8: ELECTRODE PAD-   71: CURRENT SOURCE-   72: VOLTMETER

1. A magnetoresistance effect element comprising: a first ferromagneticmetal layer; a second ferromagnetic metal layer; and a tunnel barrierlayer that is sandwiched between the first and second ferromagneticmetal layers, wherein the tunnel barrier layer has a spinel structure,wherein the tunnel barrier layer comprises: at least one lattice-matchedportion that is lattice-matched with both of the first ferromagneticmetal layer and the second ferromagnetic metal layer; and at least onelattice-mismatched portion that is not lattice-matched with at least oneof the first ferromagnetic metal layer and the second ferromagneticmetal layer, and when viewed as an inverse Fourier transform image in astacking direction of a cross-sectional crystal lattice image of theinterface between the tunnel barrier layer and the first and/or thesecond ferromagnetic metal layer, a lattice-matched portion is made upof a plurality of sequential, continuously-connected lattice lines, anda lattice-mismatched portion is made up of a plurality of sequential,non-continuously-connected lattice lines and/or no lattice lines.
 2. Themagnetoresistance effect element according to claim 1, wherein a volumeratio of the lattice-matched portion with respect to a volume of theentire tunnel barrier layer is 65% to 95%.
 3. The magnetoresistanceeffect element according to claim 1, wherein the number of constituentelements in a unit cell of the divalent cation is smaller than half thatof the trivalent cation.
 4. The magnetoresistance effect elementaccording to claim 1, wherein a magnetoresistance ratio is 100% orgreater under application of a bias voltage of 1 V or greater at a roomtemperature.
 5. The magnetoresistance effect element according to claim1, wherein the first ferromagnetic metal layer has larger coercivitythan the second ferromagnetic metal layer.
 6. The magnetoresistanceeffect element according to claim 1, wherein at least one of the firstferromagnetic metal layer and the second ferromagnetic metal layer hasmagnetic anisotropy perpendicular to a stacking direction.
 7. Themagnetoresistance effect element according to claim 1, wherein at leastone of the first ferromagnetic metal layer and the second ferromagneticmetal layer is Co₂Mn_(1-a)Fe_(a)Al_(b)Si_(1-b) (0≤a≤1, 0≤b≤1)
 8. Themagnetoresistance effect element according to claim 1, wherein thetunnel barrier layer is expressed by a chemical formula of AB₂O_(x)(0<x≤4), A represents a divalent cation that is either Mg or Zn, and Brepresents a trivalent cation that is either Al, Ga or In.
 9. Themagnetoresistance effect element according to claim 1, wherein cationsare arranged in a disordered manner in the spinel structure.
 10. Amethod of manufacturing a magnetoresistance effect element comprisingthe steps of: forming an under layer on a substrate; forming a firstferromagnetic metal layer on the under layer; forming a tunnel barrierlayer on the first ferromagnetic metal layer; forming a secondferromagnetic metal layer on the tunnel barrier layer; and forming a caplayer on the second ferromagnetic metal layer, wherein the step offorming a tunnel barrier layer comprises the steps of: depositing ametal thin film on the first ferromagnetic metal layer; oxidizing thedeposited metal thin film by plasma oxidation or natural oxidation byintroducing oxide; and heat treating the oxidized metal thin film, andthe step of oxidizing is performed after cooling the substrate to −70°C. to −30° C., and wherein the tunnel barrier layer comprises: at leastone lattice-matched portion that is lattice-matched with both of thefirst ferromagnetic metal layer and the second ferromagnetic metallayer; and at least one lattice-mismatched portion that is notlattice-matched with at least one of the first ferromagnetic metal layerand the second ferromagnetic metal layer, and when viewed as an inverseFourier transform image in a stacking direction of a cross-sectionalcrystal lattice image of the interface between the tunnel barrier layerand the first and/or the second ferromagnetic metal layer, alattice-matched portion is made up of a plurality of sequential,continuously-connected lattice lines, and a lattice-mismatched portionis made up of a plurality of sequential, non-continuously-connectedlattice lines and/or no lattice lines.